In digital subscriber line (xDSL) systems such as asymmetric digital subscriber line (ADSL) and very-high-bitrate digital subscriber line (VDSL) systems, retransmission (ReTx) can be optionally utilized for ensuring quality of transmission for latency-insensitive data, such as video. Retransmission at the physical layer (PHY) may provide improved impulse noise protection over merely using forward error correction, interleaving, and/or other approaches. The retransmission scheme used in xDSL systems supports both asynchronous transfer mode (ATM) and packet transfer mode (PTM) protocols and has been designed such that elementary frames that can be retransmitted are formed in the physical layer. Generally, for ADSL systems, it has been proposed that retransmission be implemented only in the downstream direction, whereas for VDSL systems, retransmission may either be implemented in strictly the downstream direction or in both the downstream and upstream directions.
Generally, a transmitter that supports a retransmission scheme includes a retransmission queue for storing elementary frames in order to have access to previously-sent elementary frames in the event that a request for retransmission is received. A request for retransmission is contained in a retransmission return channel (RRC) message, which contains information on which elementary frames have been correctly and/or incorrectly received, and hence identify the frames that need to be retransmitted. RRC messages are transported over the retransmission return channel. A receiver that supports retransmission will typically include a frame error detector, a rescheduling queue, and a retransmission request encoder. The frame error detector detects the correctness of each received frame. The rescheduling queue re-sequences elementary frames in the event that correctly received elementary frames are received out of order due to retransmission. The request encoder converts the decisions of the frame error detector into a RRC message, which can be understood by the transmitter side. A protocol for performing retransmission is provided in the G.998.4 recommendation. However, the G.998.4 recommendation does not support on-line reconfiguration resulting in data rate change.